The present invention relates to interfaces between optical and electrical signals, and more particularly to a cryogenic optical/electrical interconnect module for providing a high-speed optical to electrical interface from an optical fiber array to a photodiode array at cryogenic temperatures.
It is difficult to align an array of optical fibers to an array of photodiodes for use at cryogenic temperatures. Each fiber must be correctly aligned with the corresponding photodiode to a precision of approximately ten micrometers. Also the alignment, which can only be conveniently accomplished near room temperature, must remain true as the resulting module is cooled to cryogenic temperatures--less than seventy degrees Kelvin.
Prior optical/electrical interconnects, as described by P. R. Haugen et al in Optical Interconnects for High Speed Computing, Optical Engineering 25(10), 1076-1085, 1985, use silicon V-grooves to provide optical fiber captivation for alignment purposes. An angle polished fiber end is used to direct the optical output through the side of the fiber using total internal reflection, as originally described by D. R. Smith et al in P-I-N/F.E.T. Hybrid Optical Receiver for Longer-Wavelength Optical Communication Systems, Electronics Letters, 16(2), 69-71, 1980. However these prior optical/electrical interconnects make no effort to match thermal coefficients of gallium arsenide and silicon with the package.
What is desired is a cryogenic optical/electrical interconnect module that provides optical coupling between an array of fibers and an array of photodiodes and is easily alignable at one temperature while staying aligned through major temperature excursions.